1. Field of the Invention
The present invention relates to microwave ovens, and more particularly, to an air circulating structure in a microwave oven for cooling components of the microwave oven.
2. Description of the Related Art
In general, the microwave oven (MWO) disturbs molecular arrangement of microwave (approx. 2,450 MHz), to heat the food with a heat from friction between molecules caused by the disturbance.
In general, the microwave oven is provided with a main cabinet 10 having a base plate 11, an outer case 12, and a rear panel 13, an inner case 20 having a cooking chamber therein, and an outfit chamber 30 for fitting various electronic components.
FIG. 1 illustrates a related art microwave oven having the outfit chamber 30 under the inner case 20, schematically. In general, the components of a microwave oven generate much heat, which is cooled with air supplied from an exterior. However, uniform circulation of air throughout an entire space, which is divided into an upper space and a lower space, of the microwave oven is difficult practically. Consequently, an optimal air circulating structure is required. Such an air circulating structure will be described in detail.
Referring to FIG. 2, basically, the air circulating structure in the related art microwave oven is provided with two cooling fans 41 and 42 provided in a front part of a bottom of the base plate 11. One of the cooling fans (“a first cooling fan”) 41 cools various electronic components 31, and the other one of the cooling fan (“a second cooling fan”) 42 blows air to a magnetron 50 and into the inner case 20. The cooling fans 41 and 42 are driven by fan motors 41a and 42a, and a partition plate 60 separates a flow path of the air blown from the cooling fans 41 and 42.
There are a plurality of slits of air inlet openings 11a in a front part of the base plate 11, and as shown in FIGS. 1 and 5, a plurality of air outlet openings 13a and 13b in an upper part and a lower part of the rear panel 13. Air having cooled the various components 31 is discharged through the lower air outlet openings (“a first air outlet) 13a, and air having circulated through an inner case 20 is discharged through the upper air outlet openings (“second of outlet openings) 13b. 
Referring to FIGS. 3 and 4, there are a plurality air inlet holes 21 in one side wall surface of the inner case 20, and a plurality of air outlet holes 22 in an upper surface of the inner case 20. There is a cover part 23 over the inner case 20, which also serves as a guide passage of the air from the air outlet holes 22 to the second air outlet openings 22.
A process of air circulation in the related art microwave oven will be described in more detail.
When the microwave oven is put into operation, one pair of the cooling fans 41 and 42 are driven, to draw external air. Drawn external air is introduced into a space the cooling fans a provided thereto through the air inlet openings 11a, and discharged to the outfit chamber 30 and a space the magnetron 50 is provided therein through independent flow passages by the first cooling fan 41 and the second cooling fan 42, respectively.
The air blown by the first cooling fan 41 flows through the outfit chamber 30, and cools the various electronic components 31, and is discharged to an outside of the main cabinet 10 through the first air outlet opening 13a. 
Referring to FIG. 3, the air blown by the second cooling fan 42 passes through, and cools the magnetron 50. Then, referring to FIG. 4, the air flows through an inside of the inner case 20 through air inlet holes 21 in the wall surface of the inner case 20.
Then, the air is discharged to an outside of the inner case 20 through the air outlet holes 22, guided by the cover part 23, and discharged to an outside of the main cabinet 10 through the second air outlet openings 13b in the rear panel.
However, the related art microwave oven has the following problems.
First, the air circulation structure of the related art microwave oven requires a plurality of cooling fans 41 and 42 and fan motors 41a and 41b for cooling the electronic components and removal of moisture from the cooking chamber, resulting in a complicate structure and high cost.
Second, the mounting of the fan motors 41a and 42a and the cooling fans 41 and 42 in the front part of the main cabinet 10 causes direct transmission of unpleasant noise to the user.
Third, currently application of an inverter to microwave oven becomes wider gradually for varying an output of the microwave from the magnetron. However, the inverter increases overheating and damaging the various components in the microwave oven because the inverter is controlled such that the magnetron is in operation at a high power continuously. Particularly, the overheating of the inverter may cause a serious damage to various circuits. Thus, a microwave oven having the inverter applied thereto requires a structure for smooth cooling of the inverter, without fail.
Fourth, there may be serious damage to the various electronic components caused by overheating coming from a sharp temperature rise of the inverter when the microwave oven stops together with the fans which cool an inside of the microwave oven when the heat in the inverter can not be dissipated.